The present invention relates to a hybrid drive apparatus for motor vehicles, especially buses or the like required to make frequent stops. Such vehicles are conventionally equipped with a drive train arranged in the direction of the longitudinal axis of the vehicle, whereby the prime mover or engine, the clutch and the automatic transmission are arranged in series. Such vehicles are also known to use a flywheel energy storage mechanism which may be coupled to the drive train by means of a separate clutch.
German Patent Publication (DOS) No. 1,812,480 discloses a drive mechanism of the above type. It is the purpose of such drive mechanisms to be used in vehicles employed for a so-called stop and go operation, for example, on buses running along established inner city lines stopping at every other block. As the brake is applied in operating such stop and go vehicles some of the brake power is recovered by charging up a flywheel. The energy stored in the flywheel is then employed as an auxiliary source of energy in addition to the prime mover, for accelerating the vehicle.
One problem with prior art hybrid drive systems of this type resides in the fact that the flywheel is supposed to deliver energy when its r.p.m. is diminishing, such energy being used to increase the r.p.m. of the drive train. On the other hand, the flywheel is supposed to increase its r.p.m. in order to store energy from the brake operation of the vehicle at which the r.p.m. of the drive train is diminishing. These two situations are actually incompatible with each other. Therefore, prior art systems of this type have frequently included a mechanism for transforming the mechanical energy into electrical energy or into hydraulic energy. The means employed for this purpose of energy transformation made the entire drive apparatus complicated. An alternative to the energy transformation involved the use of complicated gear trains interposed between the flywheel and the drive train. Such gear trains substantially increased the overall structural length of the drive train and required too much space. Another disadvantage of prior art devices is seen in that they have a very large additional structural weight which reduces or substantially limits the payload of vehicles equipped with such mechanisms. Besides, such additional weight would in turn substantially use up the energy which would be saved by the use of the flywheel operation. As a result, the so-called hybrid drive employing a flywheel has not found heretofore any practical use worth mentioning.